1. Field of the Invention
The present invention relates to a radiation image detecting device for detecting a radiation image and a drive control method thereof.
2. Description Related to the Prior Art
A radiation imaging system, e.g. an X-ray imaging system is constituted of an X-ray generation device for generating X-rays and an X-ray imaging device for capturing an X-ray image of a subject. The X-ray generation device has an X-ray source for applying X-rays toward the subject, an X-ray source controller for controlling the drive of the X-ray source, and an irradiation switch for inputting an X-ray irradiation start command. The X-ray imaging device has an X-ray image detecting device for detecting the X-ray image formed from the X-rays which have passed through the subject, and an imaging controller for controlling the drive of the X-ray image detecting device.
The X-ray image detecting devices provided with a flat panel detector (FPD) instead of an X-ray film or an imaging plate (IP) as an X-ray detector have recently been used. Pixels that accumulate signal charge corresponding to an amount of incident X-rays are arranged in a matrix in the FPD. The FPD accumulates the signal charge on a pixel-by-pixel basis, and converts the accumulated signal charge into a voltage signal in a processing circuit, thereby detecting an X-ray image of the subject. The FPD then outputs the X-ray image as digital image data.
Portable X-ray image detecting devices (hereinafter, referred to as the electronic cassette) incorporating the FPD in a rectangular parallelepiped case have also been practically used. The electronic cassette is attached to an imaging support designed for a film cassette or an IP cassette for use. Besides that, the electronic cassette is placed on a bed or held by the subject and used to capture an area which is difficult to capture using a fixed type of X-ray image detecting device. Moreover, the electronic cassette is used outside the hospital where there are no equipments like the imaging support for housebound elderly or people injured in an accident or disaster.
Conventionally, an operation signal generated by the irradiation switch is sent to both the X-ray generation device and the X-ray imaging device as a synchronization signal for indicating a start of X-ray irradiation. Owing to this, timing that the X-rays are emitted from the X-ray source upon depression of the irradiation switch and timing that an operation for accumulating the signal charge by the X-ray image detecting device is started are synchronized. In this case, the X-ray generation device and the X-ray imaging device need to be electrically connected to each other so as to send the synchronization signal. If the manufactures of the X-ray generation device and the X-ray imaging device are different from each other and their connection interfaces (e.g. specification of a cable or connector, format of the synchronization signal) do not comply with each other, appropriate interfaces need to be newly prepared.
To solve the above problem, a technique in which the X-ray image detecting device itself detects the start of the X-ray irradiation without receiving the synchronization signal (without electrically connecting the X-ray generation device and the X-ray imaging device), and is synchronized with the X-ray generation device is proposed (see Japanese Patent Laid-Open Publication No. 2010-121944).
According to the Japanese Patent Laid-Open Publication No. 2010-121944, the start of the X-ray irradiation is detected by monitoring current on a bias line which applies a bias voltage to each pixel in view of that the current corresponding to the electric charge generated in the pixels flows on the bias line. In the Japanese Patent Laid-Open Publication No. 2010-121944, there are provided a sleep mode and an image capture mode. In the sleep mode, electric power is not supplied to the pixels. In the image capture mode, electric power is supplied to the pixels so that images can be captured. The sleep mode is switched to the image capture mode in accordance with a changeover signal from a console or an operation detection signal from the irradiation switch.
After being switched to the image capture mode, the FPD is repeatedly made to perform a readout operation for reading out the signal charge from the pixels. Then, data of frame at which the start of the X-ray irradiation is detected and data of the successive frame added up is eventually outputted as image data.
In a case where the sleep mode is switched to the image capture mode according to the switchover signal from the console, and the FPD is repeatedly made to perform the readout operation like the case of the Japanese Patent Laid-Open Publication No. 2010-121944, the readout operation before detecting the start of the X-ray irradiation is wasted and the power consumption for the wasted operation runs up. If a battery is loaded on the electronic cassette and the communication with the imaging controller is made wirelessly, the increase of the power consumption may lead frequent battery exchange, which is troublesome.
In a case where the mode is switched according to the operation detection signal from the irradiation switch, the X-ray generation device and the X-ray imaging device need to be electrically connected, which is fundamentally contradicted to the configuration in which the start of the X-ray irradiation is detected by the X-ray image detecting device itself.